Allylic end group

Figure 22 H NMR spectrum from di-hydroxyl end-capped PPG. Inset shows expansion of spectrum indicating assignments for allyl end groups of polymer.

Figure 23 Monitoring of isomerisation of allyl end groups of PPG to isopropenyl functionality over time by means of h NMR spectroscopy (a) 0 h, (b) 89 h and (c) 594 h. Reproduced from Ref. [56] with permission of John Wiley Sons, Inc.

The synthetic pathway of PE-g-PS graft copolymer via the coordination copolymerization of ethylene with PS macromonomers has been prepared using a Pd complex [111]. oj-Vinylbcnzyl PS macromonomers could not be incorporated into PE chains. On the other hand, the incorporation of -allyl PS macromonomers was achieved. It has also been reported on the comparison of the ease of incorporation of PS macromonomers among [Pg.108]

Differently, in the case of secondary chain growth with bis(phenoxy-imine)titanium catalysts, Coates and coworkers reported that chain release occurs exclusively by /3-H hydride transfer from the terminal methyl. This generates an allylic end group as shown in Scheme 15,160 and it has been utilized to produce functionalized syndiotactic propylene oligomers.258... 

The unsaturated chain end-group, C1CH2-CH=CH—, is identified by H NMR the C1CH2 proton signal resonates at 4.05 4.10 ppm. Its formation is explained by the following reaction scheme as a head-to-head addition occurs, the radical isomerizes to a secondary radical, which releases a chlorine radical to form the allylic end-group.139... 

A one-pot process to displace the halogen end groups by allyl end groups was developed using allyl tri-n-butyltin. The reaction of an alkyl halide with allyl tri-n-butyltin is a radical reaction that tolerates the presence of other functional groups such as acetals, ethers, epoxides, and hydroxyl groups. This technique was also used for the deshalogenation of polymers prepared by ATRP (Scheme 19). 

The presence of tertiary Cl also could not be confirmed in another recent study (36), which involved attempts to determine the total labile halogens content of PVC by UV analysis after phenolysis. Since the number of labile halogens found was inversely proportional to polymer molecular weight, the authors (36) suggested that most of these halogens occur in allylic end-group structures (see below). 

Allyllithium was used to polymerize hexamethylcyclotrisiloxane, D3 (eq. 16). Subsequent termination (eq. 17) with chlorotrimethylsilane yielded polydimethyl-siloxane (PDMS) macromonomers carrying allyl end groups (55). 

Another potential photochemical route to prepare telechelics is the photolysis of copolymers of MMA with various vinylketones. Upon irradiation these copolymers imdergo chain scission almost entirely by a Norrish Type I process, giving oligomers with allylic end groups (464,465). 

FIGURE 17.16 Possible orientations of the coordinated monomer and the allylic end group of the growing polymer chain around the metal center in diene polymerization with monocyclopentadienyl titanium catalyst systems (a) endo-endo (prone-prone) (b) endo-exo (prone-supine) (c) exo-endo (supine-prone) (d) exo-exo (supine-supine). (Reprinted with permission from Peluso, A. Improta, R. Zambelli, A. Organometallics 2000,19, 411-419. Copyright 2000 American Chemical Society.)... 

If a coordination vacancy is available in cis-position to the bonded polydiene chain, the a-allyl end group will tend to out itself into the more stable but temporarily inactive tt or n -allyl (Cotton s notation(2)) situation (fig. 1). 

Macromonomers with Activated Allyl End Groups Synthesis and Copolymerization... 

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